Light emitting diode containing oxidized metal contacts

ABSTRACT

A method of forming a light emitting device includes forming a semiconductor light emitting diode, forming a metal layer stack including a first metal layer and a second metal layer on the light emitting diode, and oxidizing the metal layer stack to form transparent conductive layer including at least one conductive metal oxide.

RELATED APPLICATIONS

The instant application claims the benefit of priority of U.S.Provisional Application No. 62/569,256 filed on Oct. 6, 2017, the entirecontents of which are incorporated herein by reference.

FIELD

The present invention relates to light emitting devices, andparticularly to nanowire-based light emitting diodes employing oxidizedmetal contacts, a direct view display device employing the same, andmethods of fabricating the same.

BACKGROUND

Light emitting devices such as light emitting diodes (LEDs) are used inelectronic displays, such as backlights in liquid crystal displayslocated in laptops or televisions. Light emitting devices include lightemitting diodes (LEDs) and various other types of electronic devicesconfigured to emit light.

SUMMARY

According to one embodiment, a method of forming a first light emittingdiode comprises forming a growth mask layer having an opening over a topsurface of the doped compound semiconductor layer, forming asemiconductor core through the opening in the growth mask layer, formingan active region over the semiconductor core, forming a secondconductivity type semiconductor material layer over the active region,forming a metal layer stack including a first metal layer and a secondmetal layer on the second conductivity type semiconductor materiallayer, and oxidizing the metal layer stack to form a transparentconductive layer including at least one conductive metal oxide.

According to another embodiment, a method of forming a first lightemitting diode comprises forming a first conductivity type semiconductormaterial region over a substrate, forming an active region over thefirst conductivity type semiconductor material region, forming a secondconductivity type semiconductor material layer over the active region,forming a nickel layer having a thickness in a range from 1 nm to 10 nmon the second conductivity type semiconductor material layer, forming agold having a thickness in a range from 1 nm to 10 nm on the nickellayer, and oxidizing the nickel layer at an elevated temperature to formtransparent conductive layer comprising nickel oxide while diffusing thegold layer into the second conductivity type semiconductor materiallayer through the nickel layer during the step of oxidizing to form agold doped semiconductor region in the second conductivity typesemiconductor material layer.

According to another embodiment a light emitting device comprises adoped compound semiconductor layer, a growth mask layer located on a topsurface of the doped compound semiconductor layer, a semiconductor coreextending from a top surface of the doped compound semiconductor layerthrough an opening in the growth mask layer, an active region locatedover the semiconductor core, a second conductivity type semiconductormaterial layer located over the active region, a transparent conductivelayer located on the second conductivity type semiconductor materiallayer and comprising nickel oxide, and a reflector layer located on thetransparent conductive layer.

According to another embodiment, a light emitting device comprises afirst conductivity type semiconductor material region, an active regionlocated over the first conductivity type semiconductor material region,a second conductivity type semiconductor material layer located over theactive region, a gold doped semiconductor region located in the secondconductivity type semiconductor material layer, a transparent conductivelayer comprising nickel oxide located in contact with the gold dopedsemiconductor region, and a reflector layer located on the transparentconductive layer.

According to another embodiment, a direct view display device comprisesa first light emitting diode bonded to a backplane, and a second lightemitting diode bonded to the backplane. The first light emitting diodeis configured to emit light of a first peak wavelength and comprises atransparent conductive layer located between a first doped semiconductorlayer and an aluminum or silver reflector layer, and the second lightemitting diode is configured to emit light of a second peak wavelengthlonger than the first peak wavelength and comprises a gold reflectorlayer directly contacting a second doped semiconductor layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a plan view of a substrate with light emitting diodes ofmultiple colors according to an embodiment of the present disclosure.

FIG. 1B is a plan view of a substrate with light emitting diodes of asame color according to an embodiment of the present disclosure.

FIG. 2A is a plan view of an exemplary structure including a substrateand a patterned growth mask layer according to an embodiment of thepresent disclosure.

FIG. 2B is a vertical cross-sectional view of the exemplary structure ofFIG. 2A.

FIG. 3 is a vertical cross-sectional view of the exemplary structureafter formation of nanowire cores according to an embodiment of thepresent disclosure.

FIG. 4 is a vertical cross-sectional view of the exemplary structureafter formation of active shells according to an embodiment of thepresent disclosure.

FIG. 5 is a vertical cross-sectional view of the exemplary structureafter formation of a second conductivity type semiconductor materiallayer according to an embodiment of the present disclosure.

FIG. 6 is a vertical cross-sectional view of the exemplary structureafter formation of a transparent conductive layer according to anembodiment of the present disclosure.

FIG. 7 is a vertical cross-sectional view of the exemplary structureafter formation of a top contact electrode according to an embodiment ofthe present disclosure.

FIG. 8 is a vertical cross-sectional view of the exemplary structureafter formation of a mesa structure according to an embodiment of thepresent disclosure.

FIG. 9 is a vertical cross-sectional view of the exemplary structureafter formation of a dielectric material layer according to anembodiment of the present disclosure.

FIG. 10 is a vertical cross-sectional view of the exemplary structureafter formation of a patterned photoresist layer according to anembodiment of the present disclosure.

FIG. 11 is a vertical cross-sectional view of the exemplary structureafter formation of a reflector structure according to an embodiment ofthe present disclosure.

FIG. 12 is a vertical cross-sectional view of the exemplary structureafter removal of the patterned photoresist layer according to anembodiment of the present disclosure.

FIG. 13 is a vertical cross-sectional view of the exemplary structureafter etching unmasked portions of the dielectric material layeraccording to an embodiment of the present disclosure.

FIG. 14 is a vertical cross-sectional view of the exemplary structureafter attaching a conductive bonding structure according to anembodiment of the present disclosure.

FIG. 15 is a vertical cross-sectional view of the exemplary structureafter attaching a backplane according to an embodiment of the presentdisclosure.

FIGS. 16A to 16P are schematic vertical cross-sectional views of stepsin a method of incorporating LEDs into a display panel according to anembodiment of the present disclosure.

FIGS. 17A-17D illustrate light emitting diodes according to differentembodiments of the present disclosure.

FIGS. 18, 19 and 20 are sequential vertical cross-sectional views ofportions of embodiment light emitting diodes during manufacturingprocesses according to an embodiment of the present disclosure.

FIG. 21 is a vertical cross-sectional view of a display device accordingto an embodiment of the present disclosure.

DETAILED DESCRIPTION

As used herein, a “p-plane” means a “pyramid plane,” which can by any ofthe {1 1 01} planes in the III-nitride system, a “c-plane” represents a{0001} plane, and an “m-plane” represents any of the {1 1 00} planes.Growth rate means layer growth rate along the direction perpendicular toa growth surface when not otherwise specified.

A display device, such as a direct view display can be formed from anordered array of pixels. Each pixel can include a set of subpixels thatemit light at a respective peak wavelength. For example, a pixel caninclude a red subpixel, a green subpixel, and a blue subpixel. Eachsubpixel can include one or more light emitting diodes that emit lightof a particular wavelength. Each pixel is driven by a backplane circuitsuch that any combination of colors within a color gamut may be shown onthe display for each pixel. The display panel can be formed by a processin which LED subpixels are soldered to, or otherwise electricallyattached to, a bond pad located on a backplane. The bond pad iselectrically driven by the backplane circuit and other drivingelectronics.

In the embodiments of the present disclosure, a method for fabricationof a multicolor (e.g., three or more color) direct view display may beperformed by using light emitting devices which emit different colorlight in each pixel. In one embodiment, nanostructure (e.g., nanowire)or bulk (e.g., planar) LEDs may be used. Each LED may have a respectiveblue, green and red light emitting active region to form blue, green andred subpixels in each pixel. In another embodiment, a down convertingelement (e.g., red emitting phosphor, dye or quantum dots) can be formedover a blue or green light emitting LED to form a red emitting subpixel.In another embodiment, a blue or green light emitting nanowire LED ineach pixel is replaced with a regrown red emitting planar LED, such asan organic or inorganic red emitting planar LED to form a red emittingsubpixel.

FIG. 1A illustrates a substrate 20 on which an array of pixels 25 isfabricated. Each pixel 25 can include a plurality of subpixels (10B,10G, 10R), each of which includes a cluster of light emitting nanowiresconfigured to emit light at a respective wavelength. Each pixel 25 caninclude light emitting diodes that emit light at different wavelengths.For example, each pixel 25 can include at least one first-type lightemitting diode 10G (such as at least one green-light-emitting diode, forexample two green-light-emitting diodes) that emits light at a firstpeak wavelength (such as a peak wavelength in a range from 495 nm to 570nm), at least one second-type light emitting diode 10B (such as at leastone blue-light-emitting diode) that emits light at a second peakwavelength (such as a peak wavelength in a range from 400 nm to 495 nm),and at least one third-type light emitting diode 10R (such as at leastone red-light-emitting diode 10R) that emits light at a third peakwavelength (such as a peak wavelength in a range from 600 nm to 700 nm).The number of each type of light emitting diodes within a pixel 25 canbe selected to provide a suitable level of illumination per pixel. Forexample, plural nanowire LEDs which emit green, blue and red light areformed in each respective green, blue and red light emitting areas ofthe pixel 25. Optionally, one of the sites in the pixel 25 (e.g., thesite of one of the green-emitting LEDs 10G) may be left vacant as arepair site for later attaching a repair LED device to compensate for adefective or non-functioning LED device 10G, 10B or 10R in a particularpixel 25. A vacant site may be employed for one or more additionalfunctionalities for a display device such as touch recognition throughuse of an infrared photodiode sensor. Methods of forming light emittingdiodes having different peak wavelengths on a single semiconductorsubstrate, i.e., without stacking multiple substrates over one another,is disclosed, for example, in U.S. Pat. No. 9,054,233 B2 to Ohlsson etal, which is incorporated herein by reference in its entirety.

The pixels 25, or a subset of the subpixels (10B, 10G, 10R) can besubsequently transferred to a backplane to provide a direct view displaydevice, as will be described in more detail below. As used herein, adirect view display device refers to a display device in which eachpixel 25 includes at least one light source that generates light fromwithin upon application of a suitable electrical bias. Thus, a directview display device does not require a back light unit or a liquidcrystal material. As used herein, a “multicolor” pixel refers to a pixelthat can emit light of different peak wavelengths depending onapplication of electrical bias, and thus, inherently capable ofdisplaying multiple colors.

Alternatively, only a single type of subpixels configured to emit lightat a same peak wavelength may be formed on a substrate 20 instead ofmultiple types of subpixels (10B, 10G, 10R). FIG. 1B illustrates asubstrate 20 on which only a single type of subpixels 10G (e.g., greenlight emitting LEDs) is formed. In this case, multiple substrates 20 canbe employed as sources for multiple types of subpixels. For example, afirst substrate can include subpixels 10G of a first type that emitlight at a first wavelength, a second substrate can include subpixels10B of a second type that emit light at a second wavelength (e.g., bluelight emitting LEDs), and so on (e.g., third substrate can includesubpixels 10R of a third type that emit light at a third wavelength,such as red light emitting LEDs).

Referring to FIGS. 2A and 2B, an exemplary structure is illustrated,which is an in-process structure for fabricating monolithic multicolorpixels 25 or single color subpixels (10B, 10G or 10R) on the substrate20, such as an initial growth substrate. As used herein, an “in-process”structure refers to a structure that is subsequently modified to make afinal structure. The exemplary structure can include a stack, frombottom to top, of a support substrate 22, an optional buffer layer 24,and a doped compound semiconductor layer 26. The support substrate 22can include a single crystalline material layer that functions as atemplate for growing a single crystalline semiconductor material of thebuffer layer 24. Any single crystalline material layer can be employedfor the support substrate 22 provided that epitaxial growth of acompound semiconductor material, such as a III-V compound semiconductormaterial, from the top surface of the single crystalline material layeris possible. The support substrate 22 can include a single crystallinematerial such as Al₂O₃ (sapphire) using either basal plane or r-planegrowing surfaces, diamond, Si, Ge, GaN, AN, SiC in both wurtzite (α) andzincblende (β) forms, InN, GaP, GaAsP, GaAs, InP, ZnO, ZnS, and ZnSe.For example, the support substrate 22 can include sapphire (i.e., singlecrystalline aluminum oxide) with a suitable surface orientation.

The support substrate 22 may comprise a patterned sapphire substrate(PSS) having a patterned (e.g., rough) growth surface. Bumps, dimples,and/or angled cuts may, or may not, be provided on the top surface ofthe support substrate 22 to facilitate epitaxial growth of the singlecrystalline compound semiconductor material of the buffer layer, tofacilitate separation of the buffer layer 24 from the support substrate22 in a subsequent separation process and/or to improve the lightextraction efficiency through the buffer layer 24. If bumps and/ordimples are provided on the top surface of the support substrate 22, thelateral dimensions of each bump or each dimple can be in a range from1.5 micron to 6 micron although lesser and greater lateral dimensionscan also be employed. The center-to-center distance between neighboringpairs of bumps or dimples can be in a range from 3 microns to 15microns, although lesser and greater distances can also be employed.Various geometrical configurations can be employed for arrangement ofthe bumps or dimples. The height of the bumps and/or the depth of thedimples may be in on the order of 1 microns to 3 microns, althoughlesser and greater heights and/or depths can also be employed.

The buffer layer 24 includes a single crystalline compound semiconductormaterial such as a III-V compound semiconductor material, for example aGroup III-nitride compound semiconductor material. The depositionprocess for forming the buffer layer 24 can employ any of metalorganicvapor phase epitaxy (MOVPE), molecular beam epitaxy (MBE), hydride vaporphase epitaxy (HVPE), liquid phase epitaxy (LPE), metal-organicmolecular beam epitaxy (MOMBE), and atomic layer deposition (ALD). Thebuffer layer 24 can have a constant or a graded composition such thatthe composition of the buffer layer 24 at the interface with the supportsubstrate 22 provides a substantial lattice matching with thetwo-dimensional lattice structure of the top surface of the supportsubstrate 22. The composition of the buffer layer 24 can be graduallychanged during the deposition process. If a PSS support substrate 22 isused, then the bottom surface of the buffer layer 24 may be a patterned(i.e., rough) surface.

The materials that can be employed for a bottom portion of the bufferlayer 24 can be, for example, Ga_(1-w-x)In_(w)Al_(x)N in which w and xrange between zero and less than one, and can be zero (i.e., GaN) andare selected to match the lattice constant of the top surface of thesupport substrate 22. Optionally, As and/or P may also be included inthe material for the bottom portion of the buffer layer, in which casethe bottom portion of the buffer layer 24 can includeGa_(1-w-x)In_(w)Al_(x)N_(1-x-z)As_(y)P_(z) in which y and z between zeroand less than one, that matches the lattice constant of the top surfaceof the support substrate 22. The materials that can be employed for antop portion of the buffer layer 24 include, but are not limited to,III-V compound materials, including III-nitride materials, such asgallium nitride (GaN), aluminum nitride (AlN), indium nitride (InN),gallium aluminum nitride, and gallium indium nitride, as well as otherIII-V materials, such as gallium phosphide (GaP), gallium arsenide(GaAs), gallium antimonide (GaSb), Indium phosphide (InP), indiumarsenide (InAs), and indium antimonide (InSb).

The composition of the buffer layer 24 can gradually change between thebottom portion of the buffer layer 24 and the top portion of bufferlayer 24 such that dislocations caused by a gradual lattice parameterchange along the growth direction (vertical direction) does notpropagate to the top surface of the buffer layer 24. In one embodiment,a thin bottom portion of the buffer layer 24 less than 1 micron inthickness may be undoped or doped at a low concentration of silicon.

A high quality single crystalline surface with low defect density can beprovided at the top surface of the buffer layer 24. Optionally, the topsurface of the buffer layer 24 may be planarized to provide a planar topsurface, for example, by chemical mechanical planarization. A suitablesurface clean process can be performed after the planarization processto remove contaminants from the top surface of the buffer layer 24. Theaverage thickness of the buffer layer 24 may be in a range from 2microns to 20 microns, although lesser and greater thicknesses can alsobe employed.

The doped compound semiconductor layer 26 is subsequently formeddirectly on the top surface of the buffer layer 24. The doped compoundsemiconductor layer 26 includes a doped compound semiconductor materialhaving a doping of a first conductivity type. The first conductivitytype can be n-type or p-type. In one embodiment, the first conductivitytype can be n-type.

The doped compound semiconductor layer 26 can be lattice matched withthe single crystalline compound semiconductor material of the topportion of the buffer layer 24. The doped compound semiconductor layer26 may, or may not, include the same compound semiconductor material asthe top portion of the buffer layer 24. In one embodiment, the dopedcompound semiconductor layer 26 can include an n-doped direct band gapcompound semiconductor material. In one embodiment, the doped compoundsemiconductor layer 26 can include n-doped gallium nitride (GaN). Thedeposition process for forming doped compound semiconductor layer 26 canemploy any of metalorganic vapor phase epitaxy (MOVPE), molecular beamepitaxy (MBE), hydride vapor phase epitaxy (HVPE), liquid phase epitaxy(LPE), metal-organic molecular beam epitaxy (MOMBE), and atomic layerdeposition (ALD). The thickness of the doped compound semiconductorlayer 26 can be in a range from 100 nm to 2 microns, although lesser andgreater thicknesses can also be employed.

A patterned growth mask layer 42 can be formed on the top surface of thesubstrate 20 (e.g., on top of the doped compound semiconductor layer26). The patterned growth mask layer 42 can be formed, for example, bydepositing a dielectric material layer and patterning the dielectricmaterial layer to form openings 43 therein. For example, a siliconnitride layer, a silicon oxide layer, or a dielectric metal oxide layer(such as an aluminum oxide layer) can be formed on the top surface ofthe substrate 20. In one embodiment, the dielectric material layer caninclude a silicon nitride layer. The thickness of the dielectricmaterial layer can be in a range from 3 nm to 100 nm, although lesserand greater thicknesses can also be employed.

A photoresist layer (not shown) can be applied over the top surface ofthe dielectric material layer, and can be lithographically patterned toform openings therethrough by lithographic exposure and development. Inone embodiment, the openings in the photoresist layer can be formed as atwo-dimensional periodic array. The size and shape of each opening canbe selected to optimize the shape and size of nanowires to besubsequently formed. The pattern of the openings in the photoresistlayer can be transferred through the dielectric material layer to formthe patterned growth mask layer 42. The photoresist layer can besubsequently removed, for example, by ashing.

The patterned growth mask layer 42 includes openings 43, which may, ormay not, be arranged as a two-dimensional periodic array. The shape ofeach opening 43 may be circular, elliptical, or polygonal (such ashexagonal). A portion of the top surface of the doped compoundsemiconductor layer 26 is physically exposed underneath each opening 43through the patterned growth mask layer 42.

The maximum dimension of each opening 43 (which may be a diameter, amajor axis, or a diagonal dimension) may be in a range from 5 nm to 500nm (such as from 10 nm to 250 nm), although lesser and greaterdimensions may also be employed. The nearest neighbor distance withinthe periodic array of openings 43 can be in a range from 100 nm to 10microns, such as from 500 nm to 1 micron, although lesser and greaternearest neighbor distances can also be employed.

While only a region of the exemplary structure is illustrated herein, itis understood that the exemplary structure can laterally extend alongtwo independent horizontal directions as a two-dimensional array. Theexemplary pattern illustrated in FIG. 2A may be repeated across a regionof the substrate 20, or across the entirety of the substrate 20. Thus,multiple instances of the illustrated structures in the drawings can beformed in the exemplary structure.

Referring to FIG. 3, an array of nanowires cores 32 is grown through theopenings 43 in the patterned growth mask layer 42. Each nanowires core32 includes a doped compound semiconductor material having a doping ofthe first conductivity type, i.e., the conductivity type of doping ofthe doped compound semiconductor layer 26. The material of the nanowirescores 32 may be the same as, or may be different from, the material ofthe doped compound semiconductor layer 26. In one embodiment, the firstconductivity type can be n-type, and each nanowires core 32 includes ann-doped compound semiconductor material such as III-nitride compoundsemiconductor material, for example n-doped gallium nitride.Alternatively, any other suitable III-V or II-VI material may be used.

Each of the nanowire cores 32 can be formed with a set of substantiallyvertical sidewalls and a tip portion having angled facets, i.e., facetsthat are not horizontal and not vertical (i.e., not parallel orperpendicular to the top surface of the substrate 20). The nanowirescores 32 can be grown, for example, by selective epitaxial growth of ann-doped compound semiconductor material. The process parameters of theselective epitaxial growth process can be selected such that an n-dopedcompound semiconductor material grows upward with substantially verticalsidewalls having an m-plane outer surface and angled facets having ap-pane outer surface from each opening 43 through the patterned growthmask layer 42. Methods for growing the nanowires cores 32 through theopenings 43 in the patterned growth mask layer 42 with substantiallyvertical sidewalls and faceted tip portion are described, for example,in U.S. Pat. No. 8,664,636 to Konsek et al., U.S. Pat. No. 8,669,574 toKonsek et al., U.S. Pat. No. 9,287,443 to Konsek et al., and U.S. Pat.No. 9,281,442 to Romano et al., each of which is assigned to Glo AB andU.S. Pat. No. 8,309,439 to Seifert et al., which is assigned to QuNanoAB, all of which are incorporated herein by reference in their entirety.In one embodiment, the height of the nanowires cores 32 can be in arange from 200 nm to 5 microns, although lesser and greater heights canalso be employed. In the above described embodiment, the nanowire coregrowth step occurs through an opening 43 in a mask 42. However, anyother suitable nanowire growth regime can be utilized, such as VLSgrowth using a catalyst particle or other selective growth methods.Thus, the selective nanowire growth is therefore used to merelyexemplify rather than limit the invention.

Referring to FIG. 4, an active shell 34 is formed on each nanowires core32. The active shell 34 includes at least one semiconductor materialthat emits light upon application of a suitable electrical bias. Forexample, each active shell 34 can include a single or a multi-quantumwell (MQW) structure that emits light upon application of an electricalbias thereacross. For example, the quantum well(s) may comprise indiumgallium nitride well(s) located between gallium nitride or aluminumgallium nitride barrier layers. Alternatively, the active shell 34 caninclude any other suitable semiconductor layers or stack of layers forlight emitting diode applications provided that it can be grown on thesurfaces of the nanowires cores 32. The set of all layers within anactive shell 34 is herein referred to as an active layer. The activeshell may emit any color light, such as blue, green or red light.

A selective epitaxy process can be employed to grow the active shells34. The process parameters of the selective epitaxy process can beselected such that the active shells 34 are grown as conformalstructures having a same thickness throughout. In another embodiment,the active shells 34 can be grown as a pseudo-conformal structure inwhich the vertical portions have the same thickness throughout, andfaceted portions over the tips of the nanowires cores 32 havethicknesses that differ from the thickness of the vertical portions.Methods for growing the active shells 34 on the nanowires cores 32 aredescribed, for example, in U.S. Pat. No. 8,664,636 to Konsek et al.,U.S. Pat. No. 8,669,574 to Konsek et al., U.S. Pat. No. 9,287,443 toKonsek et al., and U.S. Pat. No. 9,281,442 to Romano et al., each ofwhich is assigned to Glo AB and U.S. Pat. No. 8,309,439 to Seifert etal., which is assigned to QuNano AB, all of which are incorporatedherein by reference in their entirety. In one embodiment, the outersurfaces of the active shells 34 can include vertical faceted surfaces(i.e., vertical sidewalls) that extend perpendicular to the top surfaceof the doped compound semiconductor layer 26, and tapered facetedsurfaces (i.e., tapered sidewalls) located at a tip of eachsemiconductor nanowire (32, 34) within the array of semiconductornanowires and adjoined to an upper edge of a respective one of thevertical faceted surfaces. In one embodiment, the vertical facetedsurfaces of the active shells 34 can include crystallographic m-planes,and the tapered faceted surfaces of the active shells 34 can includecrystallographic p-planes.

The thickness of the vertical portions of the active shells 34 can beselected such that the active shells 34 do not merge among one another.The thickness of the vertical portions of the active shells 34 (asmeasured horizontally along a radial direction) can be in a range from100 nm to 1 micron, although lesser and greater thicknesses can also beemployed. Each active shell 34 includes an active light emitting layer.The composition of the active shells 34 can be selected to emit light ata desired peak wavelength by changing the composition and strain of theactive shells 34. The active shells 34 can have the same composition andemit light of the same peak wavelength. Alternatively, multiple regionscan be provided, which have different shapes, sizes, and/orinter-opening spacing for the openings 43. In this case, the activeshells 34 can with different compositions depending on the shapes,sizes, and/or inter-opening spacing for the openings 43 within each ofthe multiple regions. The different compositions for the active shells34 can be advantageously employed to fabricate multiple types of lightemitting diodes, each emitting light at a respective peak emissionwavelength.

Each set of a nanowires core 32 and an active shell 34 that contacts,surrounds, and overlies the nanowires core 32 constitutes a nanowire(32, 34). While nanowires are described as an embodiment of thenanostructure, other nanostructures, such as nanopyramids, can also beused. The nanowires (32, 34) can be formed as a two-dimensional arrayhaving periodicity along two independent directions. Each growth regionfor the nanowires (32, 34) includes at least one subpixel (10G, 10B or10R) of the direct view display device. Each nanowire (32, 34) withinthe array extends vertically from the top surface of the doped compoundsemiconductor layer 26. Each nanowire (32, 34) within the array includesa nanowire core 32 having a doping of the first conductivity type and anactive shell 34 including a preferably undoped or intrinsic active layerwhich emits light upon application of electrical bias therethrough.

Referring to FIG. 5, a second conductivity type semiconductor materiallayer 36 is formed on the sidewalls and faceted outer surfaces of thenanowires (32, 34). The second conductivity type semiconductor materiallayer 36 includes a doped semiconductor material having a doping of asecond conductivity type, which is the opposite of the firstconductivity type. For example, if the first conductivity type isn-type, then the second conductivity type is p-type. If the firstconductivity type is p-type, then the second conductivity type isn-type.

The second conductivity type semiconductor material layer 36 can includea compound semiconductor material. The compound semiconductor materialof the second conductivity type semiconductor material layer 36 can beany suitable semiconductor material, such as p-type III-nitride compoundsemiconductor material, e.g., gallium nitride and/or aluminum galliumnitride. In one embodiment, the nanowires cores 32 can include n-dopedGaN, and the second conductivity type semiconductor material layer 36can include p-doped InGaN or GaN.

The second conductivity type semiconductor material layer 36 can beformed by selective deposition of the doped semiconductor material onthe outer surfaces of the active regions 34. For example, a selectiveepitaxy process can be employed.

During the selective deposition process (which can be a selectiveepitaxy process), discrete semiconductor material portions grow from theouter surfaces of each of the active regions until the discretesemiconductor material portions merge to form the second conductivitytype semiconductor material layer 36 as a continuous semiconductormaterial layer. In other words, duration and deposition rate of theselective deposition process can be selected so that the volumes betweenneighboring pairs of nanowires (32, 34) are filled with merged verticalportions of the second conductivity type semiconductor material layer36. For example, the control of when the second type conductivity typesemiconductor material meets can be done by controlling the volume ofthe deposited material (e.g., deposition duration and deposition rate).The desired volume can be achieved by control of individual facetrelative growth rates (process parameters such as temperature, pressure,input precursor gas ratios and/or composition of (Al,In,Ga)N material).Upon continued deposition of the doped semiconductor material on theactive shells 34, the deposited semiconductor material portions coalesceto form the second conductivity type semiconductor material layer 36 asa continuous layer contacting each active shell 34 within the array ofsemiconductor nanowires (32, 34). Each continuous cluster of nanowires(32, 34) and the second conductivity type semiconductor material layer36 comprises at least one in-process subpixel (10G, 10B or 10R) of adirect view display device.

Prior to merging, each of the discrete portions of the deposited dopedsemiconductor material can grow with faceted surfaces, which can includevertical (e.g., m-plane) faceted surfaces that are parallel to thevertical faceted surfaces of the active region 34 on which a respectivedoped semiconductor material portion grows, and tapered (e.g., p-plane)faceted surfaces that are parallel to the tapered faceted surface of theactive region 34 on which the respective doped semiconductor materialportion grows.

The growth rate at various faceted surfaces may be different during theselective epitaxy process. For example, the growth rate from them-planes prior to merging of the discrete portions of the depositeddoped semiconductor material may be in a range of 3-15 times the growthrate from the p-planes prior to merging. Merging of the m-planes betweenneighboring pairs of deposited doped semiconductor material portionsreduces the total area of remaining m-planes abruptly. Thus, the growthrate from the p-planes of the second conductivity type semiconductormaterial layer 36 (which is a continuous structure including the mergedsemiconductor material portions) may increase by a factor greater than1, which can be in a range from 2 to 6 under typical growth conditions).

The second conductivity type semiconductor material layer 36 isdeposited on vertical faceted surfaces of the active regions 34 thatextend perpendicular to the top surface of the doped compoundsemiconductor layer 26, and on tapered faceted surfaces provided at atip of each semiconductor nanowire (32, 34) within the cluster ofsemiconductor nanowires (32, 34) and adjoined to an upper edge of arespective one of the vertical faceted surfaces. In one embodiment, thesecond conductivity type semiconductor material layer 36 can includevertical seams at locations that are equidistant from outer sidewalls ofa neighboring pair of active light emitting layers of the active shells34. In some embodiments, the second conductivity type semiconductormaterial layer 36 can embed optional cavities between neighboring pairsof semiconductor nanowires (32, 34) among the array of semiconductornanowires with a same cluster. Alternatively, the cavities may not beformed.

The selective deposition of the doped semiconductor material having adoping of the second conductivity type can continue until all verticalfaceted surfaces of the second conductivity type semiconductor materiallayer 36 disappear, i.e., until p-plane faceted sidewalls of the secondconductivity type semiconductor material layer 36 extend to the topsurface of the growth mask layer 42 around a bottom periphery of thesecond conductivity type semiconductor material layer 36.

For example, the remaining vertical faceted surfaces of the secondconductivity type semiconductor material layer 36 after formation of thevertical seams can include vertical faceted sidewalls that are adjoinedamong one another to form a continuous periphery that encircles arespective cluster of semiconductor nanowires (32, 34). In this case,the growth of the second conductivity type semiconductor material layer36 perpendicular to the vertical faceted sidewalls proceeds at least atthe growth rate of tapered faceted sidewalls of the second conductivitytype semiconductor material layer 36 until the height of each verticalfaceted sidewall shrinks to zero. In this case, the growth rate from them-planes proceeds at least at the rate from the growth rate fromp-planes, and typically at a higher growth rate than the growth ratefrom the p-planes, such as by at least 10%, such as by at least 50%,such as by a factor of 2 or more, until all the en-planes disappear withgrowth of the second conductivity type semiconductor material layer 36.

The second conductivity type semiconductor material layer 36 includes ahorizontally extending portion that continuously extends horizontallyand overlies the cluster of nanowires (32, 34) and vertical portionsthat are located between neighboring pairs of nanowires (32, 34). Thehorizontally extending portion of the second conductivity typesemiconductor material layer 36 contacts faceted surfaces of thenanowires (32, 34) and has a resulting roughened or faceted surface. Thehorizontally extending portion of the second conductivity typesemiconductor material layer 36 overlies the vertical portions of thesecond conductivity type semiconductor material layer 36. Each verticalportion of the second conductivity type semiconductor material layer 36can contact a portion of the top surface of the patterned growth masklayer 42 and can be adjoined to the horizontally extending portion ofthe second conductivity type semiconductor material layer 36. Thethickness of the horizontally extending portion of the secondconductivity type semiconductor material layer 36 (as measured along thevertical direction) can be in a range from 50 nm to 2 microns, such asfrom 200 nm to 1 micron, although lesser and greater thicknesses canalso be employed.

Each second conductivity type semiconductor material layer 36 over acluster of semiconductor nanowires (32, 34) (which may be atwo-dimensional periodic array of semiconductor nanowires (32, 34)within a corresponding area) contacts sidewalls of each semiconductornanowire (32, 34) within the cluster. Faceted (e.g., tapered) sidewallsof the second conductivity type semiconductor material layer 36 adjoin atop surface of the growth mask layer 42 around a periphery of the secondconductivity type semiconductor material layer 36. In one embodiment,the periphery of the second conductivity type semiconductor materiallayer 36 that adjoins the top surface of the growth mask layer 42 canhave multiple linear segments, such as a set of six linear segmentscorresponding to six sides of a hexagon if the outer periphery of thecluster has a hexagonal shape in one embodiment. As used herein, a firstelement adjoins a second element if physical contact between the firstand second elements is at least one-dimensional (i.e., includes a curve,a line, or a surface). Alternatively, the cluster can have a rectangularor circular shape. In one embodiment, the periphery is aligned to theunderlying material crystal symmetry, such that the non-vertical p-planefacets are aligned at the periphery. This would produce a non-staggeredoutlined of the cluster, and may provide a tighter packing of theclusters (i.e., reduce the LED pitch). Each second conductivity typesemiconductor material layer 36 can be a continuous material layer andcontacting all outer surfaces of the active shells 34 of the array ofsemiconductor nanowires (32, 34) within a respective cluster ofsemiconductor nanowires (32, 34). In one embodiment, each of the facetedsidewalls of the second conductivity type semiconductor material layer36 that adjoins the top surface of the growth mask layer 42 is at a sameangle with respect the horizontal plane including the top surface of thegrowth mask layer 42. In one embodiment, the faceted sidewalls of thesecond conductivity type semiconductor material layer 36 includecrystallographic p-planes, and the top surface of the growth mask layer42 can be parallel to the crystallographic c-planes of the singlecrystalline structures in the exemplary structure. In one embodiment,each of the faceted sidewalls of the second conductivity typesemiconductor material layer 36 extends within a respectivetwo-dimensional plane from the top surface of the growth mask layer 42to a location overlying a tip of a respective outermost semiconductornanowire (32, 34) in each cluster.

Referring to FIG. 6, a transparent conductive layer 38 including atleast one transparent metal oxide material on the top surface of thesecond conductivity type semiconductor material layer 36. Thetransparent conductive layer 38 can include a stack of multipletransparent conductive layers, or can include a composite of atransition metal oxide and a noble metal. The thickness of thetransparent conductive layer 38 can be selected to provide at least 70%transmission (and preferably more than 80% transmission) for thewavelength range of the underlying light emitting diodes.

In one embodiment, the transparent conductive layer 38 can include astack of at least two transparent conductive layers (132, 134). Forexample, the transparent conductive layer 38 can include a firsttransparent conductive metal oxide layer 132 and a second transparentconductive metal layer 134. The stack of at least two transparentconductive layers (132, 134) can be formed, for example, by sequentiallydepositing a first metal layer including a first elemental metal invacuum and a second metal layer including a second metal in vacuumwithout breaking vacuum between beginning of deposition for the firstmetal and the end of deposition for the second metal. Each of the firsttransparent conductive metal oxide layer 132 and the second transparentconductive metal layer 134 can be formed as a continuous conformalmaterial layer that extends across the entire area of the secondconductivity type semiconductor material layer 36 and having a uniformthickness throughout.

In one embodiment, the first metal can include a transition metal thatforms a first transparent conductive metal oxide upon oxidation. Forexample, the first metal can be a transition metal, such as nickel, andthe thickness of the first metal as deposited can be in a range from 1nm to 10 nm, such as from 2 nm to 5 nm. The second metal can be a noblemetal, such as gold, and the thickness of the second metal as depositedcan be in a range from 1 nm to 10 nm, such as from 2 nm to 5 nm. Thefirst metal and the second metal can be sequentially deposited in a samevacuum chamber, for example, employing two separate vacuum evaporationsources, such as electron beam evaporation sources. Subsequently, theexemplary structure can be annealed in an oxidizing ambient at anelevated temperature to convert the first metal layer into the firsttransparent conductive metal oxide layer 132. The oxidizing ambient caninclude oxygen, air and/or water vapor. In one embodiment, only watervapor can be used as the sole oxidizing ambient. The elevatedtemperature of the oxidation process can be in a range from 500 degreesCelsius to 850 degrees Celsius, preferably from 550 degrees Celsius to650 degrees, Celsius although lower and higher temperatures can also beemployed. The duration of the oxidation step at the elevated temperaturemay be in a range from 5 minutes to 200 minutes, such as from 10 minutesto 60 minutes, although shorter and longer oxidation time can also beemployed.

In one embodiment, the transparent conductive layer 38 can include astack of at least two transparent conductive layers comprising a firstmetal oxide layer 132, such as a nickel oxide-containing layer, and anoverlying second noble metal layer 134, such as a gold layer.

In another embodiment, the temperature and duration of the oxidationprocess can be selected to induce complete interdiffusion of materialsbetween the first metal layer and the second metal layer during theoxidation process. In this case, the transparent conductive layer 38 caninclude a homogenized metal oxide containing composite layer including atransition metal oxide, such as nickel oxide, and a noble metal, such asgold (i.e., NiO:Au composite having NiO regions and Au regions).

In another embodiment, the temperature and duration of the oxidationprocess can be selected to induce partial interdiffusion of materialsbetween the first metal layer and the second metal layer during theoxidation process. In this case, the transparent conductive layer 38 caninclude a graded metal oxide and metal composite layer in which themetal composition has a vertical gradient. Specifically, portions of thetransparent conductive layer 38 that is more proximal to the top surfacethan to the bottom surface may have a higher concentration of the secondmetal (such as gold) than portions of the transparent conductive layer38 that is more proximal to the bottom surface than to the top surface.In other words, the concentration of nickel oxide can increase from thebottom surface to or toward the top surface.

Referring to FIG. 7, a metallic material is deposited on the top surfaceof the transparent conductive layer 38. The metallic material caninclude a reflective metal such as aluminum, silver, copper, and/orgold. The metallic material can be deposited, for example, bysputtering. The average thickness of the deposited metallic material canbe in a range from 50 nm to 500 nm, although lesser and greaterthicknesses can also be employed. A photoresist layer 57 can be appliedover the metallic material, and can be lithographically patterned tocover a center portion of each LED (e.g., each sub-pixel) to besubsequently formed. An etch process can be performed to remove unmaskedportions of the metallic material employing the photoresist layer 57 asan etch mask. The etch process can be an isotropic etch process or ananisotropic etch process, and may, or may not, be selective to thematerials of the transparent conductive layer 38. Each remaining portionof the metallic material that is patterned by the etch processconstitutes a top contact electrode 50. The photoresist layer 57 issubsequently removed, for example, by ashing.

Optionally, at least one metallic (i.e., electrically conductive)barrier layer (not shown) can be formed as a component of the topcontact electrode 50. In this case, the at least one metallic barrierlayer can be located at a top surface of the top contact electrode 50,and can be employed to facilitate subsequent bonding of a soldermaterial over the mesa structures. The at least one metallic barrierlayer includes a metal or metal alloy (i.e., metallic) material layersthat can be employed for under-bump metallurgy (UBM), i.e., a set ofmetal layers provide between a conductive bonding structure and a die.In one embodiment, the at least one metallic barrier layer can include adiffusion barrier layer and an adhesion promoter layer. Exemplarymaterials that can be employed for the diffusion barrier layer includetitanium, titanium-tungsten, titanium-platinum or tantalum. Exemplarymaterials that can be employed for the adhesion promoter layer includetungsten, platinum, or a stack of tungsten and platinum. Any otherunder-bump metallurgy known in the art can also be employed.

Referring to FIG. 8, a photoresist layer 67 can be applied over each topcontact electrode 50 and the transparent conductive layer 38, and can belithographically patterned to cover an entire area of each LED (e.g.,each sub-pixel) to be subsequently formed. Preferably, the photoresistlayer 67 is wider than the top contact electrode 50 and covers the edgesof the top contact electrode 50. An anisotropic etch process can beperformed to sequentially etch unmasked portions of the transparentconductive layer 38, the second conductivity type semiconductor materiallayer 36, the semiconductor nanowires (32, 34), the patterned growthmask layer 42, the doped compound semiconductor layer 26, and the bufferlayer 24 employing the photoresist layer 67 as an etch mask. The supportsubstrate 22 can be employed as an etch stop structure. Each set ofremaining portions of the transparent conductive layer 38, the secondconductivity type semiconductor material layer 36, the semiconductornanowires (32, 34), the patterned growth mask layer 42, the dopedcompound semiconductor layer 26, and the buffer layer 24 collectivelyconstitute a mesa structure 160. The sidewalls of the transparentconductive layer 38, the second conductivity type semiconductor materiallayer 36, the patterned growth mask layer 42, the doped compoundsemiconductor layer 26, and the buffer layer 24 can be verticallycoincident (i.e., located within a same vertical plane) for each mesastructure 160. Alternatively, the above sidewalls may be tapered ratherthan vertically coincident if a taper etch is used. Sidewalls of thenanowires cores (32, 34), if physically exposed, can be verticallycoincident with the sidewalls of the transparent conductive layer 38,the second conductivity type semiconductor material layer 36, thepatterned growth mask layer 42, the doped compound semiconductor layer26, and the buffer layer 24 in a same mesa structure 160. Thephotoresist layer 67 is subsequently removed, for example, by ashing.

Referring to FIG. 9, a dielectric material layer 60 may be depositedover the top contact electrode 50, the transparent conductive oxidelayer 38 and the second conductivity type semiconductor material layer36. The dielectric material layer 60 includes a dielectric material suchas silicon oxide, silicon nitride, a dielectric metal oxide (such asaluminum oxide), organosilicate glass, or porous variants thereof. Thedielectric material layer 60 can be transparent and can be deposited bya conformal deposition method (such as low pressure chemical vapordeposition (LPCVD) or atomic layer deposition (ALD)) or by anon-conformal deposition method (such as plasma enhanced chemical vapordeposition (PECVD) or physical vapor deposition (such as sputtering ore-beam deposition).

The dielectric material layer 60 can be formed over each mesa structure160 containing the second conductivity type semiconductor material layer36 and around each remaining group of nanowires (32, 34), andencapsulates each mesa structure 160 in combination with the supportsubstrate 22. In one embodiment, at least one remaining group ofnanowires (32, 34) in the mesa structure 160 can constitute an array ofnanowires (32, 34). In one embodiment, the dielectric material layer 60can be formed as a conformal material layer, i.e., a layer having auniform thickness throughout. The thickness of the dielectric materiallayer 60 can be in a range from 100 nm to 4 microns, such as from 200 nmto 2 microns, although lesser and greater thicknesses can also beemployed.

Referring to FIG. 10, a photoresist layer 77 can be applied over theexemplary structure, and can be lithographically patterned to cover acenter portion of each mesa structure 160, and not to cover an entireperiphery of each mesa structure 160. Portions of the surfaces of thesupport substrate 22 located between neighboring mesa structures 160 canbe covered with the patterned photoresist layer 77. In one embodiment,the uncovered areas of the exemplary structure can include annularregions located at a periphery of each mesa structure 160. The annularregions can have any suitable shape, such as a hollow rectangle(including hollow square), hollow circle, hollow ellipse, hollowhexagon, etc., shape. The annular regions can be laterally spaced fromone another by remaining portions of the photoresist layer 77 that coverunderlying portions of the support substrate 22. In one embodiment, thesidewalls of the patterned photoresist layer 77 can have a retro-taperto minimize deposition of a metallic material in a subsequent metallicmaterial deposition process.

Referring to FIG. 11, a reflector material can be deposited over thedielectric material layer 60 in regions that are not covered with thephotoresist layer 77. The reflector material can be deposited by adirection deposition method such as vacuum evaporation or physical vapordeposition. Each portion of the reflector material that is depositeddirectly on the dielectric material layer 60 constitutes a reflectorlayer 70, which can be topologically homeomorphic to a ring. Eachreflector layer 70 may comprise a hollow reflector frame which can haveany suitable shape, such as a hollow rectangle (including hollowsquare), hollow circle, hollow ellipse, hollow hexagon, etc., shape. Inone embodiment, each reflector layer 70 includes a reflective materialsuch as a metal. In one embodiment, each reflector layer 70 includes atleast one material selected from silver, aluminum, copper, and gold. Inone embodiment, the reflector material can be a thin film distributedBragg reflector (DBR) with small index changes to provide betterreflectivity. The reflector material can include at least one conductivematerial and/or at least one electrically insulating material.

Reflector material portions 71 are formed on the top surfaces of thepatterned portions of the photoresist layer 77. The thickness ofhorizontal portions of the reflector layer 70 can be in a range from 5nm to 500 nm, such as from 10 nm to 250 nm, although lesser and greaterthicknesses can also be employed.

Referring to FIG. 12, the remaining portions of the photoresist layer 77and the reflector material portions 71 thereupon can be lifted off theexemplary structure, for example, by dissolving the photoresist layer 77in a solvent.

Referring to FIG. 13, an etch process can be performed to etch unmaskedportions of the dielectric material layer 60. The etch process may be ananisotropic etch process or an isotropic etch process. Portions of thedielectric material layer 60 that are not masked by the reflector layers70 (i.e., the hollow reflector frame) are removed by the etch process.The top surface of each top contact electrode 50 and the top surface ofthe support substrate 22 are physically exposed in each area that is notcovered with the reflector layers 70. A light emitting diode (LED) 10 isprovided, which includes a mesa structure 160, a dielectric materiallayer 60, and a reflector layer 70 having an annular configuration. TheLED can have any suitable horizontal cross sectional shape, such as arectangle (including square), circle, ellipse, hexagon, etc., shape. Thetop surface of the top contact electrode 50 is physically exposed withina hole in the reflector layer 70, and within a hole in the dielectricmaterial layer 60. The combination of the top contact electrode 50 andthe reflector layer 70 form a reflector for each LED 10. Each LED 10 canbe subsequently employed as a sub-pixel in a display device.

Referring to FIG. 14, a conductive bonding structure 431 is formed overeach mesa structure 160. In one embodiment, the conductive bondingstructures 431 can be formed directly on the at least one metallicbarrier layer, which can be a topmost layer of the top contact electrode50. The conductive bonding structures 431 include a solder material,which can include tin, and optionally includes an alloy of tin andsilver, gold, copper, bismuth, indium, zinc, and/or antimony. Theconductive bonding structures 431 can be formed as solder balls, or canbe formed as a layer stack including at least one solder material.

Referring to FIG. 15, a backplane 401 is provided, which includes abackplane substrate 400 and bonding structures 421 located thereupon. Abackplane can be an active or passive matrix backplane substrate fordriving light emitting devices. As used herein, a “backplane substrate”refers to any substrate configured to affix multiple devices thereupon.The backplane substrate 400 is a substrate onto which various devices(e.g., LEDs) can be subsequently transferred. In one embodiment, thebackplane substrate 400 can be a substrate of silicon, glass, plastic,and/or at least other material that can provide structural support tothe devices to be subsequently transferred thereupon. In one embodiment,the backplane substrate 400 may be a passive backplane substrate, inwhich metal interconnect structures 440 comprising metallization linesare present, for example, in a criss-cross grid. In some embodiments,active device circuits (such as field effect transistors) may not bepresent in the backplane substrate 400. In another embodiment, thebackplane substrate 400 may be an active backplane substrate, whichincludes metal interconnect structures 440 as a criss-cross grid ofconductive lines and further includes a device circuitry at one or moreintersections of the criss-cross grid of conductive lines. The devicecircuitry can comprise one or more transistors.

The backplane substrate 400 is disposed facing the substrate 20 (e.g.,above, below or side-to-side) and aligned such that the conductivebonding structures 431 face, and contact, a respective one of thebonding structures 421. At least one of the LEDs 10 (i.e., at least onesubpixel 10G, 10B or 10R) can be attached to the backplane 401 byinducing bonding between a respective pair of a conductive bondingstructure 432 and a bonding structure 421 (which may be a bonding pad)on the backplane 401. Local heating (for example, by laser irradiation)of the respective pair of the conductive bonding structure 432 and thebonding structure 421 can be employed to induce reflow and bonding ofthe solder material. All, or only a subset, of the LEDs 10 on thesubstrate 20 can be bonded to the backplane 401, as will be described inmore detail below with respect to FIGS. 16A to 16P.

In one embodiment, each LED 10 die is subpixel (10B, 10G or 10R) thatemits light of a given color, which may be, for example, blue, green, orred. FIGS. 16A-16P illustrate a method of incorporating the LEDs 10,such as a blue, green and/or red light emitting subpixels (10B, 10G,10R) into a single pixel of direct view display from different growthsubstrates 20 shown in FIG. 1B. The LEDs 10 can be the nanowire LEDsdescribed above, different nanowire LEDs and/or bulk (i.e., planar)LEDs. Each of the pixels comprises a red-light emitting diode 10Rconfigured to emit light at a peak wavelength in a range from 620 nm to750 nm, a green-light emitting diode 10G configured to emit light at apeak wavelength in a range from 495 nm to 570 nm, and a blue-lightemitting diode 10B configured to emit light at a peak wavelength in arange from 440 to 495 nm.

Referring to FIG. 16A, an in-process structure is illustrated, which canbe employed to form an exemplary light emitting device assembly (e.g.,direct view display) according to an embodiment of the presentdisclosure in which the

In this embodiment, the backplane substrate 400 may have a substantiallyplanar (i.e., not stepped) upper surface or a stepped upper surface. Thebond pads (421, 422, 423) can have the same height or different heights.The conductive bonding structures (431, 432, 433) can have the sameheight or different heights. The exemplary light emitting deviceassembly can include the same thickness bonding pads (421, 422, 423) forthe respective first, second and third LEDs (10B, 10G, 10R) and the sameheight for the conductive bonding structures (431, 432, 433). The bondpads (421, 422, 423) can have the same or different composition as eachother. The conductive bonding structures (431, 432, 433) can have thesame or different composition as each other.

In one embodiment, the conductive bonding structures (431, 432, 433) canbe formed on the LEDs 10 to be transferred to the backplane 401. Forexample, first light emitting diodes 10B can be the first devices to betransferred to the backplane substrate 400. The first light emittingdiodes 10B can be located on first support substrate 22, which can be afirst transfer substrate or a first-type growth substrate. Theconductive bonding structures 431 are formed on a first subset of thefirst light emitting diodes 10B, for example as described above andinclude the conductive bonding structure 431. The second conductivebonding structures 432 are formed on a second subset of the first lightemitting diodes 10B and the third conductive bonding structures 433 areformed on a third subset of the first light emitting diodes 10B.

In one embodiment, the conductive bonding structures (431, 432, 432) canbe substantially spherical, substantially ellipsoidal, or substantiallycylindrical. The maximum horizontal dimension (such as the diameter of aspherical shape or a cylindrical shape) of each conductive bondingstructures (431, 432, 433) can be in a range from 0.25 microns to 100microns (such as from 0.5 microns to 1 micron), although lesser andgreater maximum horizontal dimensions can also be employed.

Referring to FIG. 16B, the backplane 401 and the assembly including thefirst light emitting diodes 10B are positioned such that each conductivebonding structure 431 is attached to one first LED 10B, and contacts therespective bonding pad 421. Each second conductive bonding structure 432can be attached to the another first LED 10B and contacts the secondbonding pad 422. Each third conductive bonding structure 433 is attachedto yet another first LED 10R and contacts the third bonding pad 423.

A heating laser 467 can be employed to reflow the first conductivebonding structures 431. The heating laser 467 can have a wavelength thatinduces greater absorption of energy within the material of theconductive bonding structures (431, 432, 433) than within the materialsof the support substrate 22 or within the materials of the devices to betransferred (e.g., the first LEDs 10B). For example, the heating laser467 can have a wavelength in a range from 0.8 micron to 20 microns, suchas 1 to 2 microns, to provide a differential heating between thematerial of the conductive bonding structures 431 which are to bereflowed and the material of the conductive bonding structures 432, 433which are not to be reflowed. Differential heating is also providedbetween the conductive bonding structures 431 and the materials of thesupport substrate 22 and the devices to be transferred. The firstconductive bonding structures 431 can be selectively heated bysequential irradiation of a laser beam from the heating laser 467 toreflow each first conductive bonding structure 431, and to bond eachfirst conductive bonding structure 431 to an overlying first LED 10B andto an underlying first bonding pad 421. Preferably, the laser beam isprovided through the support substrate 22. The laser beam may betransmitted through the support substrate 22 and through the devices tothe reflector layer 82 which absorbs the laser beam and heats theadjacent conductive bonding structures 431 for selective heating andreflow. Alternatively, the laser beam may be absorbed by the supportsubstrate or the device adjacent to the conductive bonding structures431 to selectively heat and reflow the conductive bonding structures 431without reflowing the remaining conductive bonding structures (432,433).

Referring to FIG. 16C, a laser irradiation process is performed toseparate each bonded first LED 10B from the first support substrate. Thewavelength of the laser 477 (which is herein referred to an “ablationlaser”) can be different (e.g., shorter) from the wavelength of theheating laser 467, for example between 0.1 and 0.75 micron, such as 0.25to 0.5 micron. The laser provides more heating to the material of theablation material layer 130 than to the materials of the supportsubstrate 22 and the transferred devices (e.g., the first light emittingdiodes 10B). The ablation material layer 130 may comprise thesemiconductor buffer layer 24 (e.g., gallium nitride layer) describedabove or another material, such as a laser radiation absorptiveinsulating release layer (e.g., silicon rich silicon nitride layer).Each portion of the ablation material layer 130 overlying the firstconductive bonding structures 431 can be sequentially irradiated by alaser beam from the laser 477 to dissociate each underlying first LED10B.

Referring to FIG. 16D, the assembly of the first support substrate 22and attached first light emitting diodes 10B (i.e., the complement ofthe first subset of the first light emitting diodes 10B) is separatedfrom the backplane 401 and the first subset of the first light emittingdiodes 10B.

Referring to FIG. 16E, a dummy substrate 700 can employed to push thefirst light emitting diodes 10B on the first conductive bondingstructures 431 toward the backplane 401 while optionally thermallyreflowing the first conductive bonding structures 431. The compressiblefirst conductive bonding structures can be compressed by 5 to 20% oftheir thickness during this step.

Referring to FIG. 16F, a second support substrate (such as a secondgrowth or transfer substrate) 22G from which a first subset of secondLEDs 10G are removed is positioned over the in-process exemplary lightemitting device assembly, and is aligned such that a second subset ofthe second light emitting diodes 10G overlies the second bonding pads422.

Referring to FIG. 16G, the backplane 401 and the assembly including thesecond light emitting diodes 10G are positioned such that each secondconductive bonding structure 432 is attached to the second LED 10G andcontacts the second bonding pad 422.

In one embodiment, each second conductive bonding structure 432 can beattached to one of an overlying second LED 10G, and the second bondingpad 422, and each third conductive bonding structure 433 can be attachedto one of an overlying second LED 10G and contacts the third bonding pad423.

A heating laser 467 is employed to reflow the second conductive bondingstructures 432 without reflowing the remaining conductive bondingstructures (431, 433). The heating laser 467 can have a wavelength thatinduces greater absorption of energy within the material of theconductive bonding structures (431, 432, 433) than within the materialsof the support substrate 22G or within the materials of the devices tobe transferred (e.g., the second LEDs 10G). The same heating laser canbe employed as in the processing steps of FIG. 16B. The secondconductive bonding structures 432 can be sequentially irradiated by alaser beam from the heating laser 467 to reflow each second conductivebonding structure 432, and to bond each second conductive bondingstructure 432 to an overlying second LED 10G and to an underlying secondbonding pad 422.

Referring to FIG. 16H, a laser irradiation process is performed toseparate each bonded second LED 10G from the second support substrate.The wavelength of the laser 477 can be different from the wavelength ofthe heating laser 467, and provides more heating to the material of theablation material layer 130 than to the materials of the supportsubstrate 22G and the transferred devices (e.g., the second lightemitting diodes 10G). Each portion of the ablation material layer 130overlying the second conductive bonding structures 432 can besequentially irradiated by a laser beam from the laser 477 to dissociateeach underlying second LED 10G.

Referring to FIG. 16I, the assembly of the second support substrate 22Gand attached second light emitting diodes 10G (a third subset of thesecond light emitting diodes 10G that remain on the second supportsubstrate) is separated from the backplane 401 and the second subset ofthe second light emitting diodes 10G that are now attached to thebackplane 401. Referring to FIG. 16J, a dummy substrate 700 can employedto push the second light emitting diodes 10G on the second conductivebonding structures 432 toward the backplane 401 in the same manner asdescribed above. Referring to FIG. 16K, a third support substrate (suchas a third transfer substrate 22R), from which a first subset and asecond subset of third LEDs 10R have been removed in prior processingsteps, is positioned over the in-process fourth exemplary light emittingdevice assembly, and is aligned such that a third subset of the thirdlight emitting diodes 10R overlies the third bonding pads 423.

Referring to FIG. 16L, the backplane 401 and the assembly including thethird light emitting diodes 10R are positioned such that each thirdconductive bonding structure 433 is attached a third LED 10R andcontacts the third bonding pad 423. If any addition conductive bondingstructures (not shown) are present, additional conductive bondingstructures (not shown) overlying such additional bonding pads cancontact underlying additional bonding pads and overlying third LEDs 10R,and can be attached to the underlying additional bonding pads or to theoverlying third LEDs 10R.

A heating laser 467 is employed to reflow the third conductive bondingstructures 433. The heating laser 467 can have a wavelength that inducesgreater absorption of energy within the material of the third conductivebonding structures 433 than within the materials of the supportsubstrate 22R or within the materials of the devices to be transferred(e.g., the third LEDs 10R). The same heating laser can be employed as inthe processing steps of FIG. 16B or FIG. 16G. The third conductivebonding structures 433 can be sequentially irradiated by a laser beamfrom the heating laser 467 to reflow each third conductive bondingstructure 433, and to bond each third conductive bonding structure 433to an overlying third LED 10R and to an underlying third bonding pad423.

Referring to FIG. 16M, a laser irradiation process is performed toseparate each bonded third LED 10R from the third support substrate inthe same manner as in the processing steps of FIG. 15A.

Referring to FIG. 16N, a dummy substrate 700 may be employed to push thethird light emitting diodes 10R on the third conductive bondingstructures 433 toward the backplane 401. The assembly of the thirdsupport substrate 22R and any remaining third light emitting diodes 10R,if any, is separated from the backplane 401 and the third subset of thethird light emitting diodes 10R that are now attached to the backplane401 in the same manner as above. The first, second and third LEDs (10B,10G, 10R) attached to the backplane 401 have co-planar top and bottomsurfaces (e.g., top surfaces which deviate by less than 0.25 microns(e.g., 0 to 0.2 microns) from a first common plane and bottom surfaceswhich deviate by less than 0.25 (e.g., 0 to 0.2 microns) microns from asecond common plane due to the compressible conductive bondingstructures.

Referring to FIG. 16O, a dielectric matrix 445 can be applied in thespaces between the light emitting diode subpixels (10B, 10G, 10R) thatare bonded to the backplane 401. While FIG. 16O illustrates only threesubpixels (10B, 10G, 10R), it is understood that an array of pixels isformed on the backplane 401, and each pixel includes a set of lightemitting diodes such as a blue-light emitting diode as a first LEDsubpixel 10B, a green-light emitting diode as a second LED subpixel 10G,and a red-light emitting diode as a third LED subpixel 10R. Thedielectric matrix 445 can laterally surround each of the red-lightemitting diodes, the green-light emitting diodes, and the blue lightemitting diodes within the array of pixels. The dielectric matrix 445can include a self-planarizing dielectric material such as spin-on glass(SOG) or polymer, or can be planarized by a recess etch or chemicalmechanical planarization. The top surface of the dielectric matrix 445as planarized can be within the horizontal plane including the topsurfaces of the subpixels (10B. 10G, 10R), or can be vertically recessedbelow the horizontal plane including the top surfaces of the subpixels(10B. 10G, 10R).

Referring to FIG. 16P, a front side transparent conductive oxide layer450 can be formed over the dielectric matrix 445 and directly on theelectrical nodes that are located on top of each subpixel (10B, 10G,10R). For example, the front side transparent conductive oxide layer 450can be deposited on the semiconductor buffer layer 24 or directly on thecompound semiconductor material layer 26 of the first conductivity type.For example, if the buffer layer 24 has a high resistivity and is notremoved during the laser ablation step described above, then anadditional etch back or CMP is performed to remove the buffer layer 24and expose the doped compound semiconductor layer 26 of the firstconductivity type.

In this case, the front side transparent conductive oxide layer 450 canbe a common ground electrode for each of the red-light emitting diodesubpixels 10R, the green-light emitting diode subpixels 10G, and theblue-light emitting diode subpixels 10B. The subpixels 10R, 10B, 10Gform a pixel 125 of a direct view display device 500.

An optional transparent passivation dielectric layer 452 can be formedover the front side transparent conductive oxide layer 450. Thetransparent passivation dielectric layer 452 can include silicon nitrideor silicon oxide. Thus, the LED subpixels 10B, 10G and 10R are so-calledbottom emitting, vertical LEDs 10 which emit light through the compoundsemiconductor material layer 26, the front side transparent conductiveoxide layer 450 and transparent passivation dielectric layer 452. TheLEDs are vertical devices because they have electrical contacts (i.e.,the front side transparent conductive oxide layer 450 and bondingstructures or pads (431, 432, 433)) on opposite sides of each LED (10B,10G, 10R).

According to one embodiment of the present disclosure, a light emittingdevice, such as the LED 10, comprises a substrate 20 including a dopedcompound semiconductor layer 26, a growth mask layer 42 located on a topsurface of the doped compound semiconductor layer 26, semiconductornanowires (32, 34) extending from a top surface of the doped compoundsemiconductor layer 26, and a second conductivity type semiconductormaterial layer 36 located over, and around, the semiconductor nanowires(32, 34) and contacting sidewalls of each semiconductor nanowire (32,34) within each cluster of semiconductor nanowires (32, 34). Eachsemiconductor nanowire comprises nanowire core 32 of a firstconductivity type extending through a respective opening 43 through thegrowth mask layer 42, and an active light emitting shell 34. Facetedsidewalls of the second conductivity type semiconductor material layer36 adjoin a top surface of the growth mask layer 42 around a peripheryof the second conductivity type semiconductor material layer 36, and thefaceted sidewalls of the second conductivity type semiconductor materiallayer 36 include crystallographic p-planes.

Each light emitting diode (LED) 10 can have a length of 1 to 5 micronsparallel to a top surface of the doped compound semiconductor layer 26.The second conductivity type semiconductor material layer 36 is acontinuous material layer within each LED 10, and contacts all outersurfaces of the active light emitting shells 34 within each LED 10.

The outer surfaces of the active light emitting shells 34 includevertical m-plane faceted surfaces that extend perpendicular to the topsurface of the doped compound semiconductor layer 26, and taperedp-plane faceted surfaces located at a tip of each semiconductor nanowireand adjoined to an upper edge of a respective one of the verticalm-plane faceted surfaces.

Each of the faceted sidewalls of the second conductivity typesemiconductor material layer 36 that adjoins the top surface of thegrowth mask layer 42 is at a same angle with respect a plane includingthe top surface of the growth mask layer 42. Each of the facetedsidewalls of the second conductivity type semiconductor material layer36 extends within a respective two-dimensional plane from the topsurface of the growth mask layer 42 to a location overlying a tip of arespective outermost semiconductor nanowire (32, 34) within a cluster ofsemiconductor nanowires.

Generally, the exemplary LEDs 10 of the present disclosure can beemployed to form a direct view display device 500 shown in FIG. 16P. Inthis case, a backplane 401 with bonding structures (421, 422, 423) canbe employed. Each of the bonding structures (421, 422, 423) iselectrically connected to a respective one of metal interconnectstructures 440 located within, or on, the backplane 401. Multipleinstances of the LED 10 are provided as subpixels. Each instance of theLED 10 can be bonded to a respective bonding structure (421, 422, 423)on the backplane 401. Each bonded instance of the LED subpixel emitslight at a given peak wavelength for a respective pixel 125 of thedirect view display device 500.

Thus, each LED 10 is electrically connected to a respective one of themetal interconnect structures 440 and constitutes a first subpixel(e.g., 10B) which emits light at a first peak wavelength (e.g., blue) ofa respective pixel of the direct view display device. The respectivepixel further comprises a second subpixel 10G comprising a second LED 10which emits light at a second peak wavelength (e.g., green) differentfrom the first peak wavelength, and a third subpixel 10R comprising athird LED 10 which emits light at a third peak wavelength (e.g., red)different from the first and the second peak wavelengths.

Each instance of the first LED subpixel 10B can be electricallyconnected to a respective one of the metal interconnect structures 440and constitutes a subpixel which emits light at a first peak wavelengthfor a respective pixel. Multiple instances of a second LED subpixel 10Gcan be provided, which includes a same set of components as the firstLED subpixel 10B with a modification that the active layer of the secondLED subpixel 10G is configured to emit light at a second peak wavelengththat is different from the first wavelength. Each instance of the secondLED subpixel 10G is electrically connected to a respective one of themetal interconnect structures 440 and constitutes another subpixel for arespective pixel. Likewise, multiple instances of a third LED subpixel10R can be provided, which includes a same set of components as thefirst LED subpixel 10B with a modification that the active layer of thethird LED subpixel 10R is configured to emit light at a third peakwavelength that is different from the first wavelength and from thesecond wavelength. Each instance of the third LED subpixel 10R iselectrically connected to a respective one of the metal interconnectstructures 440 and constitutes yet another subpixel for a respectivepixel. The direct view display device can be a multicolor direct viewdisplay device in which each pixel comprises a plurality of subpixelswhich emits light at different wavelengths (e.g., red, green and bluelight).

Referring to FIG. 17A, an exemplary structure of a first embodiment isillustrated at a processing step after the processing steps of FIG. 5and prior to the processing steps of FIG. 6. Generally, at least onesemiconductor nanowire light emitting diode can be provided as describedabove. Typically, a plurality of semiconductor nanowire light emittingdiodes can be formed on a substrate 20 or on a plurality of substrates20. Each semiconductor nanowire light emitting diode can be provided byforming a nanowire core 32 having a doping of a first conductivity type(such as n-type), forming an active shell 34 around the nanostructurecore 32, and forming a second conductivity type semiconductor materiallayer 36 having a doping of a second conductivity type (such as p-type)over the active shell 34. The second conductivity type semiconductormaterial layer 36 can be formed over a plurality of active shells 34laterally surrounding a respective nanowire core 32.

In alternative embodiments, each light emitting diode 10 is not ananowire light emitting diode. For example, in a second embodiment shownin FIG. 17B, each area for a light emitting diode 10 includes arespective single opening in the patterned growth mask layer 42.Alternatively, in a third embodiment shown in FIG. 17C, each area for alight emitting diode 10 includes a respective array of openings in thepatterned growth mask layer 42. In a fourth embodiment shown in FIG.17D, the patterned growth mask layer 42 is not employed. In thisembodiment, continuous planar semiconductor layers are formed on then-doped compound semiconductor substrate layer 26.

In the second embodiment illustrated in FIG. 17B, the n-doped compoundsemiconductor region 32 comprises a semiconductor core which can beformed as a microdisc. As used herein, a disc refers to a structuralelement having a top surface and a bottom surface that are parallel toeach other and the area of the top surface is greater than the totalarea of surfaces (such as faceted surfaces or sidewall surfaces) thatare not parallel to the top surface. A “microdisc” refers to a disc forwhich the maximum lateral dimension of the top surface is at least 1micron and is less than 1 mm. A microdisc may have a circular, oval orpolygonal (e.g., rectangular, hexagonal, etc.) when viewed from above.

In the third embodiment illustrated in FIG. 17C, the n-doped compoundsemiconductor regions 32 comprises semiconductor cores which can beformed as nanodiscs. A “nanodisc” refers to a disc for which the maximumlateral dimension of the top surface is at least 1 nm and less than 1micron. A cluster of microdiscs or nanodiscs can be formed for each areaof a light emitting diode 10.

In the fourth embodiment illustrated in FIG. 17D, the epitaxy of then-doped compound semiconductor region 32 may be performed withoutemploying a patterned growth mask 42 on all physically exposed surfacesof an array of patterned portions of the n-doped compound semiconductorsubstrate layer 26. In this fourth embodiment, n-doped compoundsemiconductor region 32 comprises a continuous planar semiconductorlayer.

Subsequently, an active region 34 including an optically active compoundsemiconductor layer stack configured to emit light is formed on eachn-doped compound semiconductor region 32 in the first, second, third orfourth embodiments of respective FIGS. 17A-17D as described above. Ap-doped semiconductor material layer 36 is formed on the planar topsurfaces and faceted outer surfaces of the active region 34 in thefirst, second or third embodiments of respective FIGS. 17A-17C asdescribed above. A p-doped semiconductor material layer 36 is formed onthe planar top surface the active region 34 in the fourth embodiment ofFIG. 17D.

A metal layer stack 38′ including a first metal layer 232 and a secondmetal layer 134 is formed on the p-doped semiconductor material layer 36in the light emitting diodes 10 of the first, second, third or fourthembodiments of respective FIGS. 17A-17D. The first metal layer 232comprises, and may consist essentially of, an elemental metal that formsa conductive metal oxide upon oxidation. In one aspect, the first metallayer 232 comprises, and may consist essentially of nickel and has athickness of 1 nm to 10 nm, such as 1 nm to 5 nm, for example 2 nm to 3nm. The first metal layer 232 may be substantially free of oxygen. Inone aspect, the second metal layer 134 comprises, and may consistessentially of gold, and has a thickness in a range from 1 nm to 10 nm,such as 1 nm to 5 nm, for example 2 nm to 3 nm. In one aspect, the metallayer stack 38′ can be formed by vacuum evaporating the first metallayer 232 followed by vacuum evaporating the second metal layer 134without breaking vacuum between vacuum evaporating the first metal layer232 and vacuum evaporating the second metal layer 134.

FIG. 18 illustrates a close up of the metal layer stack 38′ in a portionof the light emitting diode of any of the first, second, third or fourthembodiment of respective FIG. 17A, 17B, 17C or 17D.

FIG. 19 illustrates the result of an oxidation step of the metal layerstack 38′ of FIG. 18. Due to the low thickness of metal layers 232 and134 (e.g., 10 nm or less, such as 1 to 5 nm), the first metal layer 232can be oxidized to form a transparent conductive layer 132 comprising aconductive metal oxide material, such as nickel oxide. In oneembodiment, the step of oxidizing the first metal layer 232 comprisesoxidizing the metal layer stack 38′ in an ambient comprising watervapor. The temperature can be elevated to accelerate the oxidationprocess. For example, the elevated temperature may be in a range from500 degrees Celsius to 800 degrees Celsius, although lower and highertemperatures can also be employed.

In one embodiment, the gold atoms of the second metal layer 134 diffusethrough the thin first metal layer 232 during the oxidation process intothe p-doped semiconductor material layer 36 to form a dopedsemiconductor region 131 at the top of the p-doped semiconductormaterial layer 36. For example, if the p-doped semiconductor materiallayer 36 comprises a Group III-nitride semiconductor material, such asGaN, InGaN, AlGaN or InAlGaN, and the second metal layer 134 comprisesgold, then the doped semiconductor region 131 comprises a gold dopedIII-nitride semiconductor region, such as a gold doped GaN, InGaN, AlGaNor InAlGaN region. Due to the low thickness of the second metal layer134, the entire volume of the second material layer 134 can be diffusedinto the doped semiconductor region 131. Thus, at least 90 atomicpercent, such as 90 to 99.99 atomic percent of the entire second metallayer 134 is diffused into the doped semiconductor region 131, such thatthe no second metal layer 134 remains on top of the transparentconductive layer 132. The transparent conductive layer 132 may compriseless than 10 atomic percent gold, such as zero to 5 atomic percent gold,such as 0.1 to 1 atomic percent gold, and 90 to 100 atomic percentnickel oxide.

The transparent conductive layer 132 is an electrically conductive layerand passes light in the visible wavelength range. For example, more than90%, such as more than 97%, of the light can pass through thetransparent conductive layer 132 within the visible wavelength range,i.e., in the wavelength range from 400 nm to 800 nm. The transparentconductive layer 132 can have a thickness of 1 nm to 10 nm, such as 1 nmto 5 nm, for example 2 nm to 3 nm. The doped semiconductor region 131can have a thickness of 0.1 nm to 1 nm, such as 0.2 nm to 0.8 nm.

Referring to FIG. 20, a reflector layer 70 is formed on the transparentconductive layer 132. The reflector layer 70 may comprise aluminum orsilver and have a thickness of 10 nm to 3 microns, such as 100 nm to 2microns. The process then proceeds as described above with respect toFIGS. 14 to 16P.

In a fifth embodiment shown in FIG. 21, a device contains light emittingdiodes 10 emitting light of different peak wavelengths located on thesame support. For example, the device of the fifth embodiment mayinclude a direct view display device 500 illustrated in FIG. 16Pcontaining at least one first-type light emitting diode 10G (such as atleast one green-light-emitting diode), that emits light at a first peakwavelength (such as a peak wavelength in a range from 495 nm to 570 nm),at least one second-type light emitting diode 10B (such as at least oneblue-light-emitting diode) that emits light at a second peak wavelength(such as a peak wavelength in a range from 400 nm to 495 nm), and atleast one third-type light emitting diode 10R (such as at least onered-light-emitting diode 10R) that emits light at a third peakwavelength (such as a peak wavelength in a range from 600 nm to 700 nm)located on the same backplane 401. Each light emitting diode (10G, 10B,10R) can have the configuration of any one of the first, second, thirdor fourth embodiments illustrated in FIG. 17A, 17B, 17C or 17D,respectively. The light emitting diodes 10 in FIG. 21 are shownschematically by dashed lines to indicate that they can include any typeof light emitting diode, and only the regions of the transparentconductive layers and reflector layers are shown in detail.

The shorter wavelength light emitting diodes, such as the LEDs that emitlight at a peak wavelength in range from 440 nm to 599 nm (such as theblue and/or green-light-emitting diodes 10B and/or 10G) have a differenttransparent conductive and reflector layers from the longer wavelengthlight emitting diodes, such as the LEDs that emit light at a peakwavelength in range from 600 nm to 750 nm (such as thered-light-emitting diodes 10R).

For example, the shorter wavelength light emitting diodes (e.g., 10Band/or 10G) may have the structure described above with respect to FIG.20. Specifically, each the shorter wavelength light emitting diodes(e.g., 10B and/or 10G) may have the gold doped semiconductor region 131located in the p-doped semiconductor material layer 36, an aluminum orsilver reflector layer 70 and a transparent conductive layer 132 or 134located between the p-doped semiconductor material layer 36 and thealuminum or silver reflector layer 70. The transparent conductive layer132 or 134 may comprise either the nickel oxide transparent conductivelayer 132 described above or a thin gold layer 134 having a thickness of10 nm or less, such as 1 nm to 5 nm. The gold layer 134 is transparentto visible light due to its small thickness.

In contrast, the longer wavelength light emitting diodes 10R have asecond gold doped semiconductor region 231 located in the second p-dopedsemiconductor material layer 136, and a gold reflector layer 170contacting the second gold doped semiconductor region 231. The longerwavelength light emitting diodes 10R may exclude the aluminum or silverreflector layer 70 and the transparent conductive layer (e.g., thenickel oxide layer 132 and/or the thin gold layer 134). The goldreflector layer 170 does not transmit visible light due to its largerthickness of at least 100 nm, which may be 100 nm to 3 microns. The goldreflector layer 170 contains at least 90 atomic percent gold, such as 90to 100 atomic percent gold.

Without wishing to be bound by a particular theory, the inventorsbelieve that the gold reflector layer 170 causes red shifting of thelight that is reflected from the gold reflector layer 170 by pushing thedominant wavelength of the LED 10R to longer wavelength whilesuppressing the shorter wavelength tail. In other words, the peakwavelength of the light reflected from the gold reflector layer 170 isbelieved to be greater than the peak wavelength of the incident lightemitted from longer wavelength light emitting diode 10R. Thus, it isbelieved that the gold reflector layer 170 performs effective spectralmodification through differential reflectivity within the visiblewavelength range such that light emitted from the LED 10R appears morered to an observer after being reflected from the gold reflector layer170. The shorter wavelength light emitting diodes (e.g., 10B and/or 10G)emit blue light or green light, and thus, spectral modification is notdesired. Thus, a metal other than gold, such as aluminum and/or silver,can be used as the reflector layer 70 for these LEDs 10B and/or 10G.

The red shift of the center of the emission spectrum is advantageousbecause light emission efficiency decreases within an increase in theemission wavelength in compound semiconductor based light emittingdiodes. By inducing a red shift of the emission spectrum throughreflection by a gold reflector, the direct view display device cangenerate a more vivid red color to human eyes, and thus, enhance theoverall vibrancy of the color spectrum provided by the direct viewdisplay device.

As illustrated in FIG. 21, the direct view display device 500 comprisesa first light emitting diode (10G and/or 10B) bonded to a backplane 401,and a second light emitting diode 10R bonded to the backplane 401. Thefirst light emitting diode (10G and/or 10B) is configured to emit lightof a first peak wavelength and comprises a transparent conductive layer(132 or 134) located between a first doped semiconductor layer 36 and analuminum or silver reflector layer 70. The second light emitting diode10R is configured to emit light of a second peak wavelength longer thanthe first peak wavelength and comprises a gold reflector layer directly170 contacting a second doped semiconductor layer 36.

In one embodiment, the transparent conductive layer (132 or 134) in thefirst light emitting diode (10G and/or 10B) comprises at least one of agold layer 134 or a nickel oxide layer 132 having a thickness in a rangefrom 1 nm to 10 nm, and the gold reflector layer 170 of the second lightemitting diode 10R has a thickness of at least 100 nm. The first lightemitting diode (10G and/or 10B) is configured to emit blue or greenlight, and the second light emitting diode 10R is configured to emit redlight.

In one embodiment, the transparent conductive layer (132 or 134)contacts a first gold doped semiconductor region 131 in the first dopedsemiconductor layer 36 in the first light emitting diode (10G and/or10B). The gold reflector layer 170 contacts a second gold dopedsemiconductor region 231 in the second doped semiconductor layer 136 inthe second light emitting diode 10R. In one embodiment, the goldreflector 170 is configured to shift light emitted by the second lightemitted diode 10R to a higher wavelength.

Referring to various embodiments of the present disclosure, a lightemitting device 10 comprises a first conductivity type semiconductormaterial region 32, an active region 34 located over the firstconductivity type semiconductor material region 32, a secondconductivity type semiconductor material layer 36 located over theactive region 34, a gold doped semiconductor region 131 located in thesecond conductivity type semiconductor material layer 36, a transparentconductive layer comprising nickel oxide 132 located in contact with thegold doped semiconductor region 131, and a reflector layer 70 located onthe transparent conductive layer 132, as shown in FIG. 20.

In one embodiment, the light emitting device 10 comprises a first lightemitting diode (10B and/or 10G) located in a direct view display device500, as shown in FIG. 21. The reflector layer 70 may comprise a silveror aluminum reflector layer. In one embodiment, a second light emittingdiode 10R is located in the direct view display device 500. The secondlight emitting diode 10R contains a gold reflector layer 170 directlycontacting a gold doped semiconductor region 231 in a secondconductivity type semiconductor material layer 136 of the second lightemitting diode 10R.

In the first, second, third and fourth embodiments illustrated in FIGS.17A-17D, respectively, the first conductivity type semiconductormaterial region 32 comprises at least one of a semiconductor nanowirecore, a semiconductor microdisc, a semiconductor nanodisc or asemiconductor layer.

In another embodiment, a light emitting device includes a doped compoundsemiconductor layer 26, a growth mask layer 42 located on a top surfaceof the doped compound semiconductor layer 26, a semiconductor core 32extending from a top surface of the doped compound semiconductor layer26 through an opening in the growth mask layer 42, an active region 34(e.g., active region shell or active layer) located over thesemiconductor core 32, a second conductivity type semiconductor materiallayer 36 located over the active region 34, a transparent conductivelayer located (132, 38, 138) on the second conductivity typesemiconductor material layer 36 and comprising nickel oxide, and areflector layer 70 located on the transparent conductive layer (132, 38,138).

In one embodiment, the transparent conductive layer (132, 38, 138)comprises at one of an underlying nickel oxide layer and an overlyinggold layer, a composite of nickel oxide and gold or a composite ofnickel oxide and gold in which a concentration of the nickel oxideincreases from bottom toward top of the transparent conductive layer.

The semiconductor core 32 can comprise at least one of a semiconductornanowire core, a semiconductor microdisc, a semiconductor nanodisc, asdescribed above with respect to FIGS. 17A-17C, respectively.

The preceding description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the following claims and theprinciples and novel features disclosed herein.

1. A method of forming a first light emitting diode, comprising: forming a growth mask layer having an opening over a top surface of a doped compound semiconductor layer; forming a semiconductor core through the opening in the growth mask layer; forming an active region over the semiconductor core; forming a second conductivity type semiconductor material layer over the active region; forming a metal layer stack including a first metal layer and a second metal layer on the second conductivity type semiconductor material layer; and oxidizing the metal layer stack to form a transparent conductive layer including at least one conductive metal oxide.
 2. The method of claim 1, wherein: the first metal layer comprises nickel and has a thickness in a range from 1 nm to 10 nm; and the second metal layer comprises gold and has a thickness in a range from 1 nm to 10 nm.
 3. The method of claim 2, wherein: the first metal layer consists essentially of nickel; the second metal layer consists essentially of gold; forming the metal layer stack comprises vacuum evaporating the first metal layer followed by vacuum evaporating the second metal layer without breaking vacuum between vacuum evaporating the first metal layer and vacuum evaporating the second metal layer; and the step of oxidizing comprises oxidizing the metal stack in an ambient comprising water vapor.
 4. The method of claim 2, wherein the transparent conductive layer comprises one of an underlying nickel oxide layer and an overlying gold layer, a composite of nickel oxide and gold or a composite of nickel oxide and gold in which a concentration of the nickel oxide increases from bottom toward top of the transparent conductive layer.
 5. The method of claim 2, wherein: the transparent conductive layer comprises a nickel oxide layer contacting a gold doped semiconductor region in the second conductivity type semiconductor material layer; and the gold doped semiconductor region is formed by diffusion of the gold layer into the second conductivity type semiconductor material layer through the nickel layer during the step of oxidizing.
 6. The method of claim 5, further comprising forming a silver or aluminum reflector layer over the transparent conductive layer.
 7. The method of claim 6, further comprising providing the first light emitting diode into a direct view display device.
 8. The method of claim 7, further comprising providing a second light emitting diode into the direct view display device, wherein the second light emitting diode contains a gold reflector layer directly contacting a gold doped semiconductor region in a second conductivity type semiconductor material layer of the second light emitting diode.
 9. The method of claim 1, wherein the semiconductor core comprises at least one of a semiconductor nanowire core, a semiconductor nanodisc, or a semiconductor microdisc.
 10. A method of forming a first light emitting diode, comprising: forming a first conductivity type semiconductor material region over a substrate; forming an active region over the first conductivity type semiconductor material region; forming a second conductivity type semiconductor material layer over the active region; forming a nickel layer having a thickness in a range from 1 nm to 10 nm on the second conductivity type semiconductor material layer; forming a gold having a thickness in a range from 1 nm to 10 nm on the nickel layer; and oxidizing the nickel layer at an elevated temperature to form transparent conductive layer comprising nickel oxide while diffusing the gold layer into the second conductivity type semiconductor material layer through the nickel layer during the step of oxidizing to form a gold doped semiconductor region in the second conductivity type semiconductor material layer.
 11. The method of claim 10, further comprising forming a silver or aluminum reflector layer over the transparent conductive layer.
 12. The method of claim 11, further comprising providing the first light emitting diode into a direct view display device.
 13. The method of claim 12, further comprising providing a second light emitting diode into the direct view display device, wherein the second light emitting diode contains a gold reflector layer directly contacting a gold doped semiconductor region in a second conductivity type semiconductor material layer of the second light emitting diode.
 14. The method of claim 11, wherein the first conductivity type semiconductor material region comprises at least one of a semiconductor nanowire core, a semiconductor nanodisc, a semiconductor microdisc or a semiconductor layer. 15-20. (canceled)
 21. A light emitting device, comprising: a first conductivity type semiconductor material region; an active region located over the first conductivity type semiconductor material region; a second conductivity type semiconductor material layer located over the active region; a gold doped semiconductor region located in the second conductivity type semiconductor material layer; a transparent conductive layer comprising nickel oxide located in contact with the gold doped semiconductor region; and a reflector layer located on the transparent conductive layer.
 22. The light emitting device of claim 21, wherein the light emitting device comprises a first light emitting diode located in a direct view display device, and wherein the reflector layer comprises a silver or aluminum reflector layer.
 23. The light emitting device of claim 22, further comprising a second light emitting diode located in the direct view display device, wherein the second light emitting diode contains a gold reflector layer directly contacting a gold doped semiconductor region in a second conductivity type semiconductor material layer of the second light emitting diode.
 24. The light emitting device of claim 23, wherein the first conductivity type semiconductor material region comprises at least one of a semiconductor nanowire core, a semiconductor nanodisc, a semiconductor microdisc or a semiconductor layer. 